1. Technical Field of the Invention
The present invention relates to apparatuses and methods for performing high-speed electric discharge machining operations. More particularly, the present invention relates to an apparatus and a method for performing a high-speed electric discharge machining operation, wherein the apparatus is adaptable to perform a plurality of electric discharge machining operations simultaneously and in close proximity to one another, and wherein the method provides simultaneous electric discharge machining operations in close proximity to one another.
2. Description of the Related Art
Electric discharge machining (EDM), sometimes referred to as xe2x80x9celectro-discharge machiningxe2x80x9d or xe2x80x9celectrode discharge machiningxe2x80x9d, is a known process for drilling deep, small diameter holes in a metal workpiece, such as a turbine blade of a gas turbine engine. EDM operates on the principle that, if a electrically-charged EDM tool (typically, a negatively-charged copper-alloy electrode) is brought within close proximity to a electrically-charged (for example, positively-charge if the electrode is negatively-charged) workpiece which is sometimes submerged in a bath of dielectric fluid (typically, water), an electric potential difference exists between the electrode and the workpiece and a spark discharge will arc the gap therebetween, thereby eroding a small amount of material from the workpiece adjacent the electrode. If the negative charge to the electrode is in the form of a series of pulse charges, the electric potential difference between the electrode and the workpiece is systematically repeated such that spark discharges occur at a rapid rate, and a hole can be xe2x80x9cdrilledxe2x80x9d into the workpiece if the electrode is incrementally advanced into the workpiece as workpiece material is slowly eroded therefrom. The dielectric fluid assists in the formation of the spark discharges, cools the workpiece during repeated spark discharges and carries away material eroded from the workpiece.
The EDM apparatus typically includes a translatable arm connected to a precision drive device, such as a servomotor, which is adapted to advance the arm (and the electrode held thereby) linearly towards, and away from, the workpiece with high tolerances, for example, under computer control. One complete EDM drilling operation typically is a slow process, whereby the arm smoothly advances the electrode into the workpiece at a rate of only about 1 linear inch per minute, which is due to the minute amount of material that is removed from the workpiece during a single spark discharge. Accordingly, where it is desired to drill numerous holes in the workpiece, such as, for example, in the turbine component described in U.S. Pat. No. 5,605,639 to Banks, et al., it is necessary for the EDM drilling operation to be performed once for each hole, with the operator""s repositioning the workpiece relative to the electrode in between each operation. It will be apparent to one of ordinary skill in the art that such an operation is inefficient, time-consuming and increases the likelihood of adjacent hole misalignment. It is therefore desirable to provide an EDM apparatus, wherein a plurality holes can be drilled simultaneously thereby.
Attempts have been made to provide an EDM apparatus adapted to drill simultaneously a plurality of holes. For example, the aforementioned Banks ""639 patent discloses a multiple piece electrode having a plurality of rods extending therefrom in fixed spaced relation to one another for simultaneously drilling a plurality of holes thereby. However, where a new turbine component is to be manufactured having a different distribution of diffusion holes, an entirely new electrode must be constructed having the rods arranged accordingly. Therefore, it is desirable to provide an EDM apparatus including a plurality of electrodes to drill simultaneously a plurality of holes thereby, wherein the spacing between adjacent electrodes can be adjusted to permit adjustable spacing of the holes.
It is also known that, during each EDM drilling operation, the leading tip of the electrode erodes therefrom slightly, albeit at a rate which is slower than the rate at which material is eroded from the workpiece. As such, the arm of a typical EDM apparatus is equipped with a conventional chuck-type gripping device to permit the electrode to be removed therefrom and to be replaced from time-to-time, particularly, when insufficient material remains on the electrode to permit one complete EDM drilling operation. However, it is oftentimes desirable for a single electrode to perform numerous EDM drilling operations, such that replacement thereof is not required after every EDM drilling operation, but instead, replacement of a worn electrode is required only after a predetermined number of EDM drilling operations have been performed. Accordingly, it is desirable for the electrode to be of a suitable length such that, as the tip thereof is eroded therefrom, sufficient material remains thereon after a predetermined number of EDM drilling operations to permit at least one additional complete EDM drilling operation to be performed.
It has been observed that the leading tip of the electrode typically does not erode uniformly, and as a result, the hole being formed thereby tends to curve, or wander, from the intended central axis thereof. Where the hole is but one hole in an array of closely-spaced holes, such as in the arrangement of diffusion holes of the turbine component shown in the aforementioned Banks ""639 patent, curvature thereof as a result of uneven electrode wear will result in adjacent holes intersecting one another. This result becomes significantly aggravated where the hole is of a very small diameter. Accordingly, it is desirable to provide an EDM apparatus and method whereby electrode wear is uniform such that a hole formed thereby is substantially straight.
It is known to rotate, or spin, the electrode around its central axis while performing an EDM operation, such that the electrode will wear uniformly, thereby forming a substantially straight hole. For example, U.S. Pat. No. 3,764,771 to Roy teaches an EDM apparatus including a rotatable chuck which holds an electrode for performing an EDM operation. The EDM apparatus of Roy ""771 is typical of prior-art EDM apparatuses utilizing a conventional chuck-type gripping device for holding an electrode used in an EDM operation in that a locking device, such as a set screw, is used to clamp the chuck onto the electrode. Repositioning, removing or replacing the electrode from the chuck of an apparatus such as is shown in Roy ""771, requires the operator to manually manipulate the locking device, such as, by unthreading the set screw with an Allen wrench. The area surrounding the chuck, then, must be substantially free of any obstructions which would prevent the operator from gaining access to the set screw with an Allen wrench to thereby release the electrode from within the chuck. Accordingly, two or more chucks typically cannot be spaced in close proximity to one another by a distance less than a minimum distance required to permit access to each chuck""s locking device. It is therefore desirable to provide an EDM apparatus which is adaptable to perform a plurality of electric discharge machining operations simultaneously and in close proximity to one another. It is also desirable to provide a method of forming a plurality of holes in a workpiece using electric discharge machining, wherein a plurality of electric discharge machining operations are performed simultaneously and in close proximity to one another.
U.S. Pat. No. 3,919,515 to Bangs teaches a manually-manipulated mechanical locking device for clamping an electrode in a non-rotatable collet, wherein a tool, such as an Allen wrench, is not required to release the electrode from within the collet. However, it is furthermore desirable to provide an EDM apparatus, wherein an electrode may be clamped and released from a rotatable gripping device thereof without requiring manual manipulation of a mechanical locking device.
It is also desirable to provide an EDM apparatus for use in a high-speed EDM operation, wherein a high-pressure fluid, such as water, is used to automatedly actuate movable components of the apparatus.
The present invention is for an EDM apparatus which is adapted to perform a plurality of EDM operations simultaneously and in close proximity to one another and includes one or more EDM modules which are spaced along rails of the apparatus in a side-by-side arrangement. Each EDM module is adapted to hold an electrode, and preferably, a hollow electrode, for forming one hole using electric discharge machining techniques. The electrode is gripped by a spindle assembly positioned within a throughbore of the module for rotation around an axis of the throughbore. The spindle assembly includes a sleeve rotatably fitted within the throughbore and a collet received by the sleeve, which such collet is adapted, such as by longitudinal slots, to releasably grip an electrode passing through a passageway thereof.
A piston assembly is positioned within the throughbore for movement along the throughbore axis and cooperates with a closed end of the throughbore to define a sealed piston chamber therebetween. The piston chamber is in fluid communication with a source of pressurizing fluid such that, when pressurizing fluid is supplied to the piston chamber, the piston assembly moves along the throughbore axis towards the spindle assembly. The piston assembly includes a collet closer having a seat to receive a head portion of the collet, wherein movement of the piston assembly towards the spindle assembly causes the head portion of the collet to be received in the seat of the collet closer. The collet closer seat and the collet head portion are cooperatively shaped such that the collet grips the electrode for unitary rotational movement therebetween when the collet head portion is received by the collet closer seat. Relieving the piston chamber of pressurizing fluid, then, causes the piston assembly to move along the axis away from the spindle assembly, thereby releasing the electrode from the grip of the collet and allowing the electrode to be slidingly adjusted with respect thereto. The EDM module provides for repeated gripping and releasing of the electrode from the rotatable spindle without requiring manual manipulation of mechanical gripping devices, such as conventional chucks.
Because the EDM module provides a compact assembly for firmly gripping an electrode by a rotatable spindle assembly, two or more EDM modules, each of which firmly holds an electrode rotatably secured therein, to be positioned in the EDM apparatus in very close proximity to one another. The EDM apparatus preferably includes one or more rails to receive one or more EDM modules adjustably positioned therealong. Accordingly, the spacing between adjacent EDM modules is adjustable.
The spindle assembly of each EDM module includes a driven member, such as a helical gear, which is driven by a common driving member, such as a worm gear, filled within bearings in the EDM apparatus and coupled to a driving source, such as a motor. The present invention, then, provides an EDM apparatus which is adapted to perform multiple-spindle or multiple-electrode EDM operations, wherein the EDM modules are closely-spaced, which such spacing, as mentioned above, is adjustable.
It is an object of the present invention to provide an EDM apparatus, wherein a plurality holes can be drilled simultaneously thereby.
It is another object of the present invention to provide an EDM apparatus including a plurality of electrodes to drill simultaneously a plurality of holes thereby, wherein the spacing between adjacent electrodes can be adjusted to permit adjustable spacing of the holes.
It is still another object of the present invention to provide an EDM apparatus adapted to receive an electrode of a suitable length such that, as the tip of the electrode is eroded therefrom, sufficient material remains thereon after a predetermined number of EDM drilling operations to permit at least one additional complete EDM drilling operation to be performed.
It is another object of the present invention to provide an EDM apparatus and method whereby electrode wear is uniform such that a hole formed thereby is substantially straight.
It is yet another object of the present invention to provide an EDM apparatus which is adaptable to perform a plurality of electric discharge machining operations simultaneously and in close proximity to one another.
It is still another object of the present invention to provide a method of forming a plurality of holes in a workpiece using electric discharge machining, wherein a plurality of electric discharge machining operations are performed simultaneously and in close proximity to one another.
It is another object of the present invention to provide an EDM apparatus, wherein an electrode may be clamped and released from a rotatable gripping device thereof without requiring manual manipulation of a mechanical locking device.
It is yet another object of the present invention to provide an EDM apparatus for use in a high-speed EDM operation, wherein a high-pressure fluid, such as water, is used to automatedly actuate movable components of the apparatus.
These and additional objects, features and advantages of the present invention will become apparent to those reasonably skilled in the art from the description which follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the claims appended hereto.
According to one aspect of the present invention, an electric discharge machining module for forming a hole in a workpiece with an electrode is provided, comprising: a module body defining a throughbore extending along an axis; a spindle assembly at least partially positioned within the throughbore for rotation around the axis, the spindle assembly including a first electrode passageway coaxial with the axis for receiving the electrode therethrough; and, a piston assembly positioned within the throughbore for movement along the axis between a released position and an engaged position, the piston assembly including a second electrode passageway coaxial with the axis for receiving the electrode therethrough, wherein a collet closer of the piston assembly engages a collet of the spindle assembly when the piston assembly is in the engaged position such that the collet grips the electrode for unitary rotational movement of the electrode and the spindle assembly.
According to another aspect of the present invention, an electric discharge machining module for forming a hole in a workpiece with an electrode is provided, comprising: a module body defining a throughbore extending along an axis; a collet at least partially positioned within the throughbore, the collet including a first electrode passageway coaxial with the axis for receiving the electrode therethrough; and, a collet closer positioned within the throughbore for movement along the axis between a released position and an engaged position, the collet closer including a second electrode passageway coaxial with the axis for receiving the electrode therethrough, wherein the collet closer engages the collet when the collet closer is in the engaged position such that the collet grips the electrode.
According to yet another aspect of the present invention, an electric discharge machining apparatus for forming at least one hole in a workpiece with at least one electrode is provided, comprising: a housing having at least one rail; and, at least one electric discharge machining module mounted to the at least one rail for adjustable movement therealong, each of the at least one electric discharge machining module being adapted to hold one of the at least one electrode.
According to still another aspect of the present invention, a method for securing an electrode in an electric discharge machining module having a module body defining a throughbore therein, wherein the throughbore extends along an axis and is closed at one end thereof, is provided, comprising the steps of: providing a spindle assembly at least partially positioned within the throughbore, the spindle assembly having a first electrode passageway therethrough; providing a piston assembly positioned within the throughbore for movement along the axis, the piston assembly having a second electrode passageway therethrough, the piston assembly cooperating with the closed end of the throughbore to define a piston passageway therebetween; positioning the electrode through the first electrode passageway of the spindle assembly and through the second electrode passageway of piston assembly, the electrode sealingly engaging a seal surrounding a portion of the second electrode passageway of the piston to inhibit leakage of the pressurizing fluid from the piston chamber through the second electrode passageway; and, supplying pressurizing fluid to the piston chamber to urge the piston assembly towards the spindle assembly, the spindle assembly including a collet portion shaped to be received by a collet closer portion of the piston assembly such that the collet grips the electrode.